The changes in water level and flood flow to the delta were also considered to be partly influenced by flow volatility from the upstream which frequently caused consecutive small flood years from 2002 to the present, except for large floods in 2011. The course of flood in recent years also has unusual changed. The 2014 large flood appeared prior to the 2015 small flood, contrary to the law of flood operation. Floods irregularly occur up to half a month later than before and the duration of floods was shorter, especially in 2013 and 2015.
In the period from 1998-2019, the peak of flood measured at the hydrographic stations in An Giang province largely fluctuated. The year 2000 was
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the flood peak reached the highest and the year 2015 was the lowest peak. The water level in Tien and Hau's rivers measured at upstream and downstream locations in these points was significantly different. At the upstream, on the Tien River, the peak of the flood measured at Tan Chau station was 506 cm in 2000, suddenly reduced to 255 cm in 2015, while at the Hau River at Chau Doc station, the flood peak decreased correspondingly from 490 cm to 235 cm. At the same time, the flood peak measured at the downstream, on the Tien River at Cho Moi station had a sudden decrease from 358 cm to 220 cm, while on the Hau River at Long Xuyen station, a corresponding decrease from 263 cm to 216 cm (see figure 1.4).
Figure 1.4 Flooding peaks during 1998-2019 phase were measured at upstream and downstream stations in An Giang province
(Source: An Giang Committee for Incidents and Disaster Response, and Search and Rescue)
In the early 2000s, flood season in An Giang regularly appeared with great intensity and frequency. The province had issued the project 31 /ĐA.BCS and Decision 1536/QĐ-UBND "exploiting the advantages of flooding season" to help
100 150 200 250 300 350 400 450 500 550
Tân Châu Châu Đốc Chợ Mới Long Xuyên
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people mitigate losses and to live in harmony with floods. The project had positively supported for people to develop effective models and trades in the flood season such as fishing net production, aquatic vegetable planting, interwoven weaving, etc. The most striking result of the project was the harmonization of economic benefits and the environment, ensuring both increased their income and compensate alluvium and wash alum to improve their soil. Therefore, the orientation of agricultural production of the province in this period is to "live with floods" for a long time.
Due to both objective and subjective reasons, the situation of large floods has not occurred frequently in the province since 2003 up to now (except for the year of 2011) that forced the province to propose corrective measures and adapt to changes.
Implemented solutions during this period achieved certain results, helping farmers to increase income through increasing productivity and agricultural output. The policy orientation of the province was focusing on economic development, increasing agricultural production, contributing to ensuring food security but also arising a several consequences such as the depletion of land, water resources, and ecosystem destruction.
Predicted low flood situation and climate change would still be lasting in the coming decades. An Giang agriculture and aquaculture sector are and will face many potential risks, especially the significant increase in production costs, and threaten the ecological environment. Therefore, the province needs to have breakthrough solutions and strategic steps to balance economic and environmental factors, and inspires the motto of “developing agriculture associated with solutions to cope with the degradation of water resources due to climate change and the impact of water use activities in the upper VMD”.
Drought and sea level rise
Because of topography without the sea, An Giang was not affected by drought and saline intrusion over the last 5 years. However, these extreme events
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have been increasing in intensity and frequency. In particular, salinity concentration in the dry season 2015-2016 increased to 0.01-0.2 ‰ at where has a border with Kien Giang province. For the reason that the dry season in that year was the result of the abnormal low flood peaks of the year after.
According to the Department of Natural Resources and Environment of An Giang, there was a large fluctuation in water flow in the Mekong River. The unusually rapid decline in the early dry season and abnormally slow rise at the beginning of the rainy season were the main causes of drought in the upstream of VMD. The accumulation and discharge of hydropower reservoirs have altered the flow in the downstream. Although the average water flows during the dry season increased, the downstream flow changes were detrimental to agricultural production and fisheries.
Cho Moi district is located far away from the saline area, so it is not available statistics of this phenomenon impacts on the economy, society in general, and aquaculture activities in particular. In some areas, prolonged drought has led to changes in soil structure causing landslides in some areas of the district.
Tropical cyclones and depressions
The Mekong Delta is less affected by storms and tropical depressions than other regions across the country. In the period of 1951 - 2015, the whole region lightly impacted by 09 tropical storms from the East Sea (see figure 1.5), excluding from Lynda storm in 1997. That typhoon left 3,000 people dead, 200,000 houses destroyed, 83,000 people homeless and causing $385 million in economic damage (Takagi & Le Tuan Anh, 2017).
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Figure 1.5 The map of storm and depression trajectories impacted An Giang during the phase of 1951-2015
(Source: http://kttv.angiang.gov.vn/ban-do-khi-hau)
Cho Moi district is located far from the storm center, no damage statistics have been recorded in the above period. The impact of typhoons in this area was mainly the heavy rains accompanied by tornadoes, which inundated and stagnated local agricultural production activities. This phenomenon usually lasts from August to November, coinciding with the rainy season.
Heavy rain and whirlwind
In An Giang, heavy rain and whirlwind often occur from April to November, coinciding with the rainy season. These phenomena depend on the topography, periods of the rainy season. However, these extreme events have happened abnormal and unpredictable over 5 years. The consequences annually cause little damage to humans but significantly destroy local property, agriculture, and
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aquaculture. The most affected communes by whirlwinds are Tan Chau, Phu Tan, Cho Moi, Tinh Bien, and An Phu.
Cho Moi district is less affected by whirlwind compared to other localities in An Giang. Affected communes were often located along Tien and Hau rivers such as Hoi An, Binh Phuoc Xuan, Hoa Binh, Nhon My, Long Kien, Kien An, My Hoi Dong, Long Giang, and Long Dien A. Notably in 2016, a whirlwind in Cho Moi district killed 01 people, damaged 39 houses, 4.717 ha of agricultural production area, the value of the damage was about 29,937 million VND, according to Cho Moi people‟s committee.
Land erosion
Riverbank erosion is one of the threats to the lives and property of people in the Mekong Delta, which An Giang is one of the localities most seriously affected.
The time of occurrence of landslides is often in the dry season and the beginning of the rainy season. There are many causes of the serious situation in upstream provinces rather than the downstream. Mainly due to the influence of upstream dams associated with mining activities, and socioeconomic factors have made the amount of mud and sand decline seriously, reducing the possibility of sediment accumulation, change the water flow, the geological structure of the riverbank, tectonic movement of the river.
In the period of 1989-2014, the landslide in An Giang province took place at a very fast level, highest in the period 2000-2005 (average speed of 318.97 ha/year), the period of 2014-2017 was slower with average speed (28.38 ha/year). The total damaged area of this period was 3146.94 ha (Điệp, Minh, Trường, Thành, & Vinh, 2019). According to the report of An Giang Department of Natural Resources and Environment, the whole province has 52 river sections at risk of erosion, with a total length of 44,000m along Tien River, Hau River, and small tributaries of the Mekong River. For instance, 07 communes and towns were listed at risk of riverbank landslides, of the Tien River including Kien An commune, Cho Moi
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town, Long Dien A commune, My Luong town, Tan My commune, commune My Hiep, Binh Phuoc Xuan commune; with 6 communes of the Hau river: My Hoi Dong, Nhon My, An Thanh Trung, Hoa Binh, Hoa An Kien An.
Figure 1.6 A landslide scene of a riverside resident along the Vam Nao river, Cho Moi district, An Giang
(Source: baoangiang.com.vn)